This Excel spreadsheet is programmed for students to practice Kepler's 3rd law problems assigned randomly for planets in our solar system and also for the Galilean moons. This spreadsheet expires after the 2016/17 school year. Students won't get the same set of problems, necessarily, so they can't just copy their neighbor's answers. When the student successfully completes each problem and answers in the yellow cell, the cell changes color, giving the student immediate feedback, no harm, no foul. In my experience, often students need to learn how to properly use the calculator to solve these types of problems. Specifically, Kepler's 3rd law says that the square of the ratio of orbital periods of planets about the sun or moons about a planet equals the cube of the ratio of orbital radii, respectively. For the planets, this exercise uses the Earth for reference, where the period is calculated in earth years and the orbital radius is in astronomical units (au). I have taught seven years and have been incorporating this type of formative assessment the last four years. My experience has been that students like these assignments more than text problems or worksheets since they know right away if they have succeeded. Also, since the answers turn colors, they seem to be motivated to get the color change. Also, I can stand in view of the screens and tell from across the room if a student is progressing and succeeding or is having trouble. This allows me to prioritize immediately how I aid individual students. I distribute the file using Google Classroom, instructing students to open the file in Excel (Google wants you to open in Googlesheets, the default and easy option). While Googlesheets now has the formatting to change the cell colors, I have not tested in G'sheets. The first step on opening the file is to enter the value from cell A1 into cell C1. This then loads the problems in the rest of the sheet. If you want all students to have the same problems, simply enter the number in cell C1 and save and send to all students.